Method of making thin-walled reentrant structure



April 29, 1958 c. H. LLEWELLYN, JR, ETAL METHOD OF MAKING THINQWALLED REENTRANT Filed Jan. 5, 1956 STRUCTURE ATTORNEY Clay H. Llewellyn, Jr., Long Beach,

United States PatentO 2,832,676 METHOD OF MAKING THIN-WALLED REENTRANT STRUCTURE Richard D. Welsh, Orange, and Stephen A. Hays, Sierra Madre, Calif., assignors to North American Aviation, Inc.

Application January 5, 1956, Serial No. 557,595 3 Claims. (CI. 41-41) This invention is directed to a method of making a thinwalled structure having reentrant portions on the surface thereof. More particularly, this invention is directed to a method of forming an extremely flexible bellows.

Heretofore, Various thin-walled structures have been made by an electroforming operation wherein a removable, shaped mandrel is placed in the electroplating bath and a metal from the bath is electrodeposited on the surface thereof. While such process is satisfactory for flat and rounded mandrel surface shapes, much difiiculty has been experienced in forming certain shapes which include reentrant portions on the surface thereof. It has been found that the electrodeposited metal is build up at the edges of the reentrant portions and does not evenly plate to constant thickness within the reentrant portion itself.

' It has been found that extremely accurate parts with constant thickness in the reentrant portions as well as the other portions thereof can be made by subjecting the mandrel to a chemical deposition nickel plating process followed by an etching operation to remove the metal core material. It has been found that an extremely sensitive and accurate bellows having relatively deep convolutions therein can be made by the present process.

An object of this invention is to provide a process of making thin-walled structure having reentrant portions on the surface thereof.

A further object of this invention is to provide a method of making an extremely flexible bellows.

A still further object of this invention is to provide a process of making thin structures of complex shapes.

An additional object of this invention is to provide a process of making a sensitive bellows with reinforced end sections.

Another object of this invention is to provide various thin-walled structures made using an electroless nickel or electroless cobalt plating process.

Other objects of invention the following description taken in connection with the accompanying drawings, in which:

Fig. l is a sealed bellows after chemical deposition;

Fig. 2 shows a bellows portion with reinforcement after the chemical deposition;

Fig. 3 showsthe completed bellows of Fig. 2;

Fig. 4 shows a double-walled container made by the process of this invention; and v Fig. 5 shows a heat exchanger element made by the present invention. i

The method of this invention to make a thin-walled structure, having reentrant portions on the surface thereof, comprises first forming a metal core portion having an exterior configuration corresponding to a reentrant shape. A thin layer of an etch-proof dissimilar metal is then chemically deposited on the exterior of the core portion. This metal may be chosen from one of the group consisting of nickel and cobalt according to the particular use to which the thin-walled structure is to be put. After the chemical deposition, the core material is selectively etched away whereby the chemically deposited layer will become apparent from ring 22 is resistant to the etching process.

. Patented Apr. 29, 1958 forms the thin-walled structure. The details of the above process will be apparent from the following description of various thin-walled structures made by the process.

Fig. 1 shows a sealed bellows after the chemical deposition stage of the process. A metal core portion is formed by a machining, casting or other metal forming process to the desired configuration. Bore 11 is then drilled or otherwise formed centrally of the core to a depth sufficient to leave a web portion 14 at the bottom thereof. A masking 12, or other type of plug means, seals the bore 11 from the action of the chemical deposition bath. An apertured plate 9 may be fitted over the core end and itself subsequently plated as shown. Core 10 is placed within and exposed to electroless nickel or electroless cobalt deposition in a plating bath containing a nickel salt or cobalt salt and sodium hypophosphite; Prior m' the deposition process, the core material may be degreased and cleaned with acid or alkali cleaners. Various materials may be employed for the core portion. While aluminum is preferred, due to the subsequent ease of removal by the action of a suitable caustic, steel, copper,

'is placed on the exterior surface of the core 10 including an even plate in the reentrant portions 16, the plugs or masking portions 12 are removed and the' entire structure is exposed to the action of an etching agent. In the case of aluminum, a 10% sodium hydroxide solution at a temperature of to 212 F. is satisfactory. Acid etching, typically hydrochloric acid, is used if the core material is steel. It is, of course, obvious that bore 11 may be omitted from the core portion since it serves only to cut down the etching time. Thus, the core portion 10 may be solid and the ends thereof plated in the deposition process.

These ends must then be cut off to allow the'etching medium to attack the core material itself.

reinforcing end ring 22 is press-fitted or otherwise attached to the end portions of the core 20. Preferably, ring 22 has a knife edge which firmly presses into the softer aluminum core. A suitable end plug 23 is placed in the ring portion 22 to prevent subsequent plating interiorly of the core portion. The structure is then subjected to chemical deposition as above to form a' thin layer of nickel'or cobalt 'on the exterior surfaces thereof. After the plug 23 has been removed the more material is etched away leaving a bellows made up of a thin layer 24 and a reinforced end portion 22 attached thereto. It is to be understood that the material, normally steel, brass or copper, of theend The end rings for attachingthe bellows'to adjacent Difliculty in some instances is experienced in 22 serve as a means structure.

mechanically connecting the nickel or cobalt thin shell to adjacent surfaces by conventional means, 'describ ed end rings are not employed.

- -'Fig'.-'3 shows a connected bellows structure using the bellows formed in the above process. A connecting fixture having a ring portion 25 which may seat internally or externally of the reinforced ends 22 of the bellows 24 is welded, brazed, soldered or otherwise joined to such portion. Tapered portions 26 on said connecting fixture lead to a portion 27 into or onto which an inlet tube 28 is attached by any of the above means. i The extreme sensitivity and flexibility of the finished bellows can be seen in Fig. 3. The actual sensitivity is a function'of the thickness of the chemically deposited layer, the diameter when the above of the core volutions.

portion and-the number and size of the con- Fig. 4 shows an additional use of the process in making ,th in-walle.d structure having -tion'30. is firstformed in the .ree ntrant;portions as at 31.

reentrantportions. A;.porindicated configuration-with The entire-inner and outer surfaces of the core 30, except for ,the.topedge35, is

pIated with nickel or cobalt process followed by 1 removal of the core portion 30 by .etching. A double wall structure is thus obtained. Disc .means 34 may be used to 'mask the portions 35 during'the :chemical deposition process and then inserted between the neck portions tokeep the v. spaced 7 relationship.

inner and. outer thinwalls in Fig. shows a;sin gle heat exchanger element which may be. made vby the present process.

A core 40 is provided .with a;series of :cylindrical ,embossments 41 aroundthe gperiphery thereof with reentrant portions 43 therebetween.

A layer of-inickel .or cobalt portions 43. Following portion'40 is exposed to the .embossment portions ..exchanger element.

ing portions on the-ends is chemically deposited on the evenlyinto thereentrant intFig. 2 and are normally attached as thinelements on a ,heat exchanger.

The following. examples are given of the-chemical deposition steppof the present invention:

(1) .The marked core portion 20 of Fig.

bath containing grams per litre .in an .electroless nickel of sodium hypophosphite, .citrate, and 50 2 wasplaced 40 grams per litre ot-sodium grams per litreof NiSO .6H O.for..a time .sUfficientto givethedesired thickness of plate. The plat- -ing bath waskept at a temperature of from 190' to 215 at apH of from :4 to 5. A 0.001 inch. thick bellows was .formed in two hours.

A 0.0035 inch thick bellows layer wasformed after 12 hours in the above bath.

,(2) A cobalt plate was Fig. 2 by exposing a maske placed on the core portiomof cl core portion to;an electroless -cobalt deposition in a plating bath containing grams per litre of sodium hypophosphite, 100 grams per litre of am- .monium hydroxide, 100 grams per litre of sodiumcitrate,

.and grams perlitre of cobalt sulphate.

Operating conditions in this example, included a temperature .of

F. and a pH of from 9 to 11.

A. layer 0.001 was-formed after the core material had been in the :chemical deposition bath for about two hours.

(3) Av nickel-cobalt alloy portion similar to'that sho .tsulphate to the .cobalt bath described. :and varying the ratio Ofcitrate and wn in Fig. 2 by adding nickel under Example .2 hydroxide. -to give .optimum plating, characteristics.

(4) A sealed bellows, corresponding to that illustrated by placing the core portion.10 in.-a grams per litre of nickel sulphate, sodium. citrate, and 12 1 grams per in Fig. 1, was formed solution eontaining'40 grams per litre of :litre of sodium hypophosphite at 'a temperature .ofqfrom .205" -to.2l0 F. and a pH wall thickness. of 0.002 in'this bath.

of from 35 to 4.2. Abe-Hows inch was. obtained after. 6; hours Each of the above examples used an aluminum core portion which was subsequently etched away-ina 10nto 20% sodium hydroxide solution at a temperatureof190 to 200 F. fora period of from 1 to.2 hours. The :etchplate was termed on a core by thechemical deposition theexterior of: said core I portion deposition in a.plating bath containing a saltof a metal selected from: the group consisting of nickel and cobalt, .and analkalimetal'hypophosphite, chemically plating-a thin layer-of a metal .ing theresultant core .tively etching the core portion away whereby said layer forms said thin-walled structure.

a metal core portion of proofhigh strength tube plugging the. interior passageway of said core, chemically ing out of the configurations seen in Fig. 4 and Fig. 5 will normally extend over a greater time range.

Although the inventionhas been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

We claim:

1. The method of making a thin-walled structure having reentrant portions on the surface thereof comprising first forming a metal core portion having an exterior configuration including ,desired reentrantportions, chemically plating a thin layer of a dissimilar metal chosen from the group consisting of nickel and cobalt on the exterior of said core portion and into said reentrant portions, and selectively etching away the core portion whereby said layer forms said thin-walled structure.

'2. The invention as set outinclaim 1 inwhichsaid core portion is aluminum.

3. The invention .asset out in claim 1 in whichsaid core portion is steel.

4. The method of making a thin-walled structure having reentrant. portions on the surface thereof comprising .first forming a metal core portion having an exterior con figuration including desired reentrant portions, exposing to .an electrolessmetal selected from said group on said exterior. surface and into said reentrant portions removportion from said bath,-and selec- S. A method'of making a bellows comprising first forming .a' metal core portion having exterior convolutions .correspondingto a desired bellows shape, chemically plating azdissimilar metal on to a desired bellows wall ing. thecore portion away the exterior of said core portion thickness, and selectively etchwhereby said dissimilar metal forms the bellows.

6. A method of making a bellows comprising forming an etchable metal intoexterior convolutions and an interior passageway, placing anetchover at least one end of said core,

plating a dissimilar metal on the exterior of'said core and -saidtube, and etching the core portion away'whereby said plating forms a flexible bellows having a high strength end. 7. The. :invention asv set out in claim 6 in which said dissimilar. metal is nickel.

8. The invention as set outin claim 6-in which saiddissimilar. metal is. cobalt.

References Cited in the file of this patent UNITED STATES PATENTS 2,359,302 Curtis Oct. 3, 1944 2,569,453 Chester etal. Oct. 2, 1951 2,739,883 Newman Mar. 27, 1956 FOREIGN i PATENTS 2,474 Great Britain July 18,1873 

1. THE METHOD OF MAKING A THIN-WALLED STRUCTURE HAVING REENTRANT PORTIONS ON THE SURFACE THEREOF COMPRISING FIRST FORMING A METAL CORE PORTION HAVING AN EXTERIOR CONFIGURATION INCLUDING DESIRED REENTRANT PORTIONS, CHEMICALLY PLATING A THIN LAYER OF A DISSIMILAR METAL CHOSEN FROM THE GROUP CONSISTING OF NICKEL AND COBALT ON THE EXTERIOR OF SAID CORE PORTION AND INTO SAID REENTRANT PORTIONS, AND SELECTIVELY ETCHING AWAY THE CORE PORTION WHERBY SAID LAYER FORMS SAID THIN-WALLED STRUCTURE. 